Scramble code allocation method, a radio base station, a mobile station, and a mobile communications system

ABSTRACT

A scramble code allocation method used by mobile communications systems, and a base station and a mobile station that use the method are disclosed. The scramble code allocation method autonomously and optimally sets up a scramble code unique to a target base station. The method includes a step of generating a collection packet for collecting unique information of surrounding base stations, the unique information being used for setting up respective identifiers of the surrounding base stations; a step of broadcasting the collection packet to the surrounding base stations through a network; a step of receiving response packets from the surrounding base stations in response to the collection packet; a step of extracting the unique information of the surrounding base stations inserted in the response packets that are received; a step of storing the extracted unique information; and a step of setting up an identifier of the target base station based on the stored unique information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. application Ser. No. 10/981,462, filedNov. 5, 2004 and claims the benefit of priority under 35 U.S.C. § 119 ofJapanese Patent Application No. 2003-379170, filed on Nov. 7, 2003, thecontents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a scramble code allocationmethod in CDMA (Code Division Multiple Access) cellular systems, andespecially relates to a scramble code allocation method applied to aradio base station at a new installation, and while in service.

2. Description of the Related Art

In the CDMA cellular systems, methods for assigning a scramble code toeach radio base station are disclosed as follows.

According to a first conventional method, a scramble code of a radiobase station is identified by detecting a time difference (gap) betweenthe time when the scramble code is transmitted by a transmitter and thetime when the scramble code is received by a receiver. The timedifference is determined in units of chips. This is realized by using astandard time common to all apparatuses in a mobile communicationssystem, employing the GPS (Global Positioning System).

Specifically, a BTS control unit (Base Transceiver Station Controller)identifies a first radio base station. Then, the first radio basestation is made to transmit a pilot channel using a known scramble code.Then, other radio base stations, called the second through Nth radiobase stations, receive the pilot channel from the first radio basestation, detect the gap of the scramble code in units of chips, andstore the gap values. When all the second through Nth radio basestations finish storing the gap values, the first radio base stationstops transmission. Then, the second radio base station transmits apilot channel using a known scramble code, and other radio base stationsdetect and store the chip gap values. This operation is repeated untilall the N radio base stations finish the pilot channel transmission.Then, distances between each of the radio base stations is computed by apredetermined method based on the chip gap values stored in thepredetermined storing place. After computing the distances between eachof the radio base stations, a scramble code is assigned to each radiobase station based on the distances (see Patent Reference 1).

According to a second conventional method, a radio base station has asearch function that searches for sync channels transmitted by otherradio base stations (radio base stations of other cells and the like),and autonomous synchronization between the radio base stations,assignment of a scramble code, and assignment of a frequency are carriedout.

That is, the radio base station includes a scramble code identifyingunit that identifies scramble codes of other radio base stations basedon a de-scrambled signal and an output result of an A/D converter, andoutputs the identified result to a code allocating unit. The codeallocating unit outputs an optimal scramble code to the radio basestation based on the identified scramble codes of other radio basestations, and the code allocating unit assigns the optimal scramble codeto the radio base station based on the identified scramble codes (seePatent Reference 2).

[Patent reference 1] JPA 2000-32531

[Patent reference 2] JPA 2002-218528

DESCRIPTION OF THE INVENTION Problem(s) to be Solved by the Invention

Nevertheless, the conventional methods described above have thefollowing problems.

Since it is necessary to receive the pilot channel using the knownscramble code (diffusion code) from other radio base stations, areceiver for receiving the pilot channel concerned is required of a CDMAcellular system of FDD (Frequency Division Duplex) where the frequencyfor a downlink and the frequency for an uplink are different.Furthermore, since there is a limit to the receiving power of the pilotchannel of a radio base station, only scramble codes of radio basestations within the limit can be searched.

Until a scramble code is determined for a new radio base station, and aservice is started, N-1 radio base stations of the N radio base stationsof the CDMA cellular system use the predetermined known scramble code incommon, and the N radio base stations transmit a pilot channel in turn.For this reason, while the scramble code is being selected, at least theN radio base stations must stop service, that is, it takes time for theservice to start when the new radio base station is being installed anda scramble code for the new radio base station is being determined.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea scramble code allocation method, a radio base station, and a mobilestation that substantially obviate one or more of the problems caused bythe limitations and disadvantages of the related art.

A specific object of the present invention is to provide a scramble codeallocation method, a radio base station (base station), and a mobilestation of a mobile communications system, which scramble codeallocation method is for a radio base station to autonomously andoptimally set up the scramble code.

Features and advantages of the present invention are set forth in thedescription that follows, and in part will become apparent from thedescription and the accompanying drawings, or may be learned by practiceof the invention according to the teachings provided in the description.Objects as well as other features and advantages of the presentinvention will be realized and attained by the scramble code allocationmethod, the radio base station, and the mobile station particularlypointed out in the specification in such full, clear, concise, and exactterms as to enable a person having ordinary skill in the art to practicethe invention.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, the presentinvention provides as follows.

Means for Solving the Problem

The present invention provides a radio base station (a base station)that is used in a mobile communications system that includes two or moreradio base stations, and a network to which each of the radio basestations (base stations) is connected, wherein a mobile radio station(mobile station) that communicates with a base station identifies thebase station by an identifier uniquely assigned to the base station. Thebase station of the present invention includes a packet generating unitconfigured to generate a collection packet for collecting uniqueinformation of other base stations (surrounding base stations) aroundthe base station (target base station), the unique information of thesurrounding base stations being used in setting up an identifier of thetarget base station, a packet transceiving unit configured to broadcastthe collection packet to the surrounding base stations through thenetwork, and to receive response packets transmitted by the surroundingbase stations in response to the collection packet, a packet informationextracting unit configured to extract the unique information of thesurrounding base stations, the unique information being contained in theresponse packets, an updating unit configured to store the uniqueinformation, and a scramble code setting unit configured to set up anidentifier of the target base station based on the unique information ofthe surrounding base stations stored in the updating unit.

The present invention further provides a scramble code allocation methodfor the mobile communications system described above. The scramble codeallocation method includes a step of generating the collection packetfor collecting the unique information of the surrounding base stations,the unique information being used for setting up an identifier of thetarget base station, a step of broadcasting the collection packet to thesurrounding base stations through the network, a step of receiving theresponse packets from the surrounding base stations in response to thecollection packet, a step of extracting the unique information of thesurrounding base stations contained in the response packets, a step ofstoring the extracted unique information, and a step of setting up anidentifier for the target base station based on the unique informationof the surrounding base stations.

The present invention further provides a mobile station used in themobile communications system described above, wherein the mobile stationcommunicates with the target base station that is surrounded by thesurrounding base stations. The mobile station includes a packet controlunit configured to extract the unique information of the surroundingbase stations from a packet received from the target base station, theunique information being used in setting up the identifiers of thesurrounding base stations, and an information updating unit configuredto store the extracted unique information, wherein the packet controlunit transmits the stored unique information to the target base station.

The mobile station of the present invention can include a communicationsituation surveillance unit configured to supervise the quality ofcommunications with the target base station, and the communicationsituation surveillance unit can be configured to transmit informationthat the communication quality is insufficient to the target basestation.

Another aspect of the present invention provides the base station usedin the mobile communications system described as above, wherein the basestation includes a scramble code setting unit configured to set up ascramble code of the base station, a packet control unit configured toextract the unique information of the surrounding base stations frompackets transmitted by the surrounding base stations, the uniqueinformation being used for setting up the identifiers of the surroundingbase stations, and an information updating unit configured to store theextracted unique information, wherein the scramble code setting unitsets up an identifier of the base station based on the uniqueinformation collected during a predetermined period from the start ofservice.

Here, the scramble code setting unit can be arranged such that aninitial default identifier is set up when the base station is beinginitiated.

Further, the base station can include a packet generating unitconfigured to generate a collection packet for collecting the uniqueinformation that is used in setting up the identifier of the surroundingbase stations, a packet transceiving unit configured to broadcast thecollection packet to the surrounding base stations via the network, andto receive response packets transmitted by the surrounding base stationsin response to the collection packet, a packet information extractingunit configured to extract the unique information of the surroundingbase stations inserted in the response packets received, wherein thescramble code setting unit is arranged such that an identifier for thebase station is set up based on the unique information of thesurrounding base stations extracted by the packet information extractingunit, when the information that the communication quality isinsufficient is received from a mobile station.

The scramble code allocation method of the present invention includes astep for the mobile station to receive the unique information of thesurrounding base stations, the unique information being used for settingup the identifiers of the surrounding base stations, and a step for themobile station to store the unique information and to transmit theunique information to the target base station.

Further, the scramble code allocation method of the present inventionmay include a step of supervising the quality of communications with thetarget base station, and a step of transmitting to the target basestation the information that the communication quality is insufficient.

Another aspect of the present invention provides the scramble codeallocation method that includes a step of setting up an identifier ofthe target base station, and upon starting the service, a step ofreceiving the unique information from the mobile station and storing theunique information, the unique information being used in setting up theidentifiers of the surrounding base stations, and a step of measuringthe elapsed time from the start of the service, and setting up theidentifier of the target base station based on the unique informationcollected during a predetermined period.

Further, the step of starting the service may include a step of settingup an initial default identifier when the target base station isinitiated.

Another aspect of the present invention provides the scramble codeallocation method that includes a step of generating the collectionpacket for collecting the unique information of the surrounding basestations, a step of broadcasting the collection packet to thesurrounding base stations through the network, a step of receivingresponse packets in response to the collection packet from thesurrounding base stations, a step of extracting the unique informationof the surrounding base stations contained in the response packets, anda step of setting up an identifier of the target base station based onthe unique information of the surrounding base stations contained in theresponse packets when the information that the quality of communicationsis insufficient from a mobile station is received.

Further, the present invention provides a mobile communications systemthat includes two or more base stations, each being connected to anetwork, wherein a mobile station communicating with a base stationidentifies the base station by a unique identifier, one of which isassigned to every base station. The mobile station includes a packetcontrol unit configured to extract the unique information used forsetting up the identifiers of the surrounding base stations from thepacket received from the target base station, and an informationupdating unit configured to store the extracted unique information,wherein the packet control unit transmits the unique information to thetarget base station. Further, the target base station includes ascramble code setting unit configured to set up an identifier of thetarget base station, a packet control unit configured to extract theunique information used in setting up the identifiers of the surroundingbase stations from the packet received, and an information updating unitconfigured to store the extracted unique information, wherein thescramble code setting unit sets up the identifier of the target basestation based on the identification information collected during apredetermined period from the service start.

EFFECT OF THE INVENTION

According to the present invention, the base station autonomouslyselects a scramble code based on the unique information of thesurrounding base stations, eliminating the need for manually designing acommunication service area.

Further, since the unique information of the surrounding base stationsis acquired using communications between the base stations, noadditional equipment, such as a receiver for receiving a pilot channeland a synchronous channel, is required for setting up scramble codes andchip timing that are not overlapped between the base stations that areinstalled in a wide area.

Further, the base station can start providing the service as soon as itis installed, setting up the scramble code while giving the service.Accordingly, the problem in that it takes time to start the service of anew base station is solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a mobile communications system according toan embodiment of the present invention;

FIG. 2 is a block diagram of a base station of the mobile communicationssystem according to the first embodiment of the present invention;

FIG. 3 gives a block diagram and a table for explaining a CPU and a datastorage unit that constitute the base station of the mobilecommunications system according to the first embodiment of the presentinvention;

FIG. 4 is a flowchart of operations of the base station of the mobilecommunications system according to the first embodiment of the presentinvention;

FIG. 5 is another flowchart of operations of the base station of themobile communications system according to the first embodiment of thepresent invention;

FIG. 6 is a block diagram of the base station of the mobilecommunications system according to the second embodiment of the presentinvention;

FIG. 7 gives a block diagram and a table for explaining the CPU and thedata storage unit that constitute the base station of the mobilecommunications system according to the second embodiment of the presentinvention;

FIG. 8 is a flowchart of operations of the base station of the mobilecommunications system according to the second embodiment of the presentinvention;

FIG. 9 is another flowchart of operations of the base station of themobile communications system according to the second embodiment of thepresent invention;

FIG. 10 is a block diagram of the base station of the mobilecommunications system according to the third embodiment of the presentinvention;

FIG. 11 gives a block diagram and a table for explaining the CPU and thedata storage unit that constitute the base station of the mobilecommunications system according to the third embodiment of the presentinvention;

FIG. 12 is a block diagram of a mobile station of the mobilecommunications system according to the third embodiment of the presentinvention;

FIG. 13 gives a block diagram and a table for explaining the CPU and thedata storage unit that constitute the mobile station of the mobilecommunications system according to the third embodiment of the presentinvention;

FIG. 14 is a flowchart of operations of the base station of the mobilecommunications system according to the third embodiment of the presentinvention;

FIG. 15 is a flowchart of operations of the mobile station of the mobilecommunications system according to the third embodiment of the presentinvention;

FIG. 16 is a block diagram of the base station of the mobilecommunications system according to the fourth embodiment of the presentinvention;

FIG. 17 gives a block diagram and a table for explaining the CPU and thedata storage unit that constitute the base station of the mobilecommunications system according to the fourth embodiment of the presentinvention;

FIG. 18 is a block diagram of the mobile station of the mobilecommunications system according to the fourth embodiment of the presentinvention;

FIG. 19 gives a block diagram and a table for explaining the CPU and thedata storage unit that constitute the mobile station of the mobilecommunications system according to the fourth embodiment of the presentinvention;

FIG. 20 is a flowchart of operations of the base station of the mobilecommunications system according to the fourth embodiment of the presentinvention;

FIG. 21 is another flowchart of operations of the base station of themobile communications system according to the fourth embodiment of thepresent invention;

FIG. 22 is a flowchart of operations of the mobile station of the mobilecommunications system according to the fourth embodiment of the presentinvention; and

FIG. 23 is another flowchart of operations of the mobile station of themobile communications system according to the fourth embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention are describedwith reference to the accompanying drawings.

In the following, items that provide the same function bear the samereference number, and explanations thereof are not repeated.

The mobile communications system according to the first embodiment ofthe present invention is explained with reference to FIG. 1. A basestation of the mobile communications system according to the presentembodiment autonomously and optimally sets up a scramble code that isunique to the base station by recognizing scramble codes and the likecurrently used by other base stations (surrounding base stations) usingcommunications between the base stations.

The mobile communications system according to the embodiment includestwo or more base stations (BS) 1-1, 1-2, 1-3, two or more mobilestations (MS) 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and a network (communicationnetwork) 1-10 to which the base stations are connected.

The base station 1-1, 1-2, and 1-3 form service areas 1-11, 1-21, and1-31, respectively, such that communication services are provided to themobile stations 1-4, 1-5, 1-6, 1-7, 1-8, and 1-9. Communications betweena mobile station and a base station of a service area are carried out byfrequency-division duplex transmission (FDD), wherein an uplink circuituses a frequency different from a downlink circuit. Further, a codedivision multiple access method (CDMA) is used in the uplink circuitsuch that more than one mobile station can make simultaneous access tothe base station, using different orthogonal codes.

Further, in order that the mobile stations 1-4, 1-5, 1-6, 1-7, 1-8, and1-9 may identify a base station that serves the service area to whicheach of the mobile stations belong, a unique identifier (scramble code)is assigned to each of the base stations 1-1, 1-2, and 1-3.

In the CDMA cellular system according to the present embodiment, Nscramble codes are prepared, which are repeatedly assigned to the basestations.

Next, the base station of the mobile communications system according tothe present embodiment is explained with reference to FIG. 2 and FIG. 3.The base station 1-1 is equipped with a CPU (Central Processing Unit)2-1, a ROM (Read Only Memory) 2-2, a RAM (Random Access Memory) 2-3, adata storage unit 2-4, a network communications unit 2-5, and a radiocommunications unit 2-6, all of which are connected through a bus asshown in FIG. 2.

The base stations 1-2 and 1-3 have the same configuration as the basestation 1-1, and explanations thereof are not repeated.

The CPU 2-1 controls operations of the base station 1-1 according to aprogram stored in ROM 2-2. ROM 2-2 stores the program that the CPU 2-1executes. RAM 2-3 stores data required for the program execution by theCPU 2-1. The data storage unit 2-4 stores a scramble code managementtable that includes permanent data required for the mobilecommunications system, and unique information of the surrounding basestations such as the base stations 1-2 and 1-3.

An example of the scramble code management table is shown in FIG. 3. Thescramble code management table 2-41 contains information of thesurrounding base stations, such as the base stations 1-2 and 1-3. Theinformation includes an identifier uniquely assigned to each of the basestations, which can be a MAC (Media Access Control) address or an IP(Internet Protocol) address, an identifier of the scramble codescurrently used by the respective base stations, chip timing of thescramble codes, and the number of hops between the base station 1-1 andeach of the surrounding base stations.

The network communications unit 2-5 performs a process such that networkcommunications between the base stations are provided.

The radio communicating unit 2-6 performs radio communications with themobile stations through an antenna 2-7. The radio communicating unit 2-6performs processes peculiar to the radio communications, such asscrambling/de-scrambling, error correcting, coding/decoding, andmodulating/demodulating.

Further, the CPU 2-1 includes a scramble code selecting unit 3-1, aninformation updating unit 3-2 connected to the scramble code selectingunit 3-1, a packet information extracting unit 3-3 connected to theinformation updating unit 3-2, a packet transceiver unit 3-4 connectedto the packet information extracting unit 3-3, a packet generating unit3-6 connected to the packet transceiver unit 3-4, and a uniqueinformation extracting unit 3-5 connected to the packet generating unit3-6 as shown in FIG. 3.

The scramble code selecting unit 3-1 of the base station 1-1 assigns ascramble code and chip timing to be used by the base station 1-1 in sucha way that the scramble code and the chip timing for the base station1-1 are not currently used by any of the surrounding base stations withreference to the scramble code management table 2-41.

When a response packet is received from one of the surrounding basestations, the information updating unit 3-2 updates the scramble code,the chip timing of the scramble code, and the number of hops to the basestation contained in the response packet, and stores the information inthe scramble code management table 2-41.

The packet information extracting unit 3-3 extracts the uniqueinformation of the base station (the address of the base station thatgenerates the response packet, the scramble code, the chip timing of thescramble code, and the number of hops to the base station) contained inthe header and the payload of the response packet received from thesurrounding base station.

The packet transceiver unit 3-4 transmits and receives packets to/fromthe network communications unit 2-5. Further, the packet transceiverunit 3-4 performs a process peculiar to the network communications sothat communications with the surrounding base stations are provided.

The unique information extracting unit 3-5 extracts the uniqueinformation of the base station 1-1 such that a collection packet and aresponse packet can be generated. The packet generating unit 3-6generates the collection packet for collecting unique information of thesurrounding base stations in the case that the base station 1-1 is beinginitialized.

The packet generating unit 3-6 generates the response packet when thebase station 1-1 receives a collection packet from another base station.

Next, operations of the base station of the mobile communications systemaccording to the present embodiment are explained with reference to FIG.4 and FIG. 5.

When the base station 1-1 is initialized, such as by turning on thepower supply, the following process is performed. Namely, at Step S4-1,a collection packet is generated in order to collect unique informationof the surrounding base stations, such as the base stations 1-2 and 1-3.A broadcast address as a destination address, and a predetermined numberof hops (a few hops) serving as a service life period of the collectionpacket are set into the header of the collection packet. Here, no dataare inserted in the payload section of the collection packet.

Next, at Step S4-2, the generated collection packet is broadcast to thesurrounding base stations currently installed on the CDMA cellularsystem using communications between the base stations. Further, a timerfor measuring elapsed time of a predetermined period is started when thecollection packet is broadcast.

Then, at Step S4-3, the base station 1-1 that broadcasts the collectionpacket to the surrounding base stations determines whether a responsepacket has been received from any of the surrounding base stations, suchas the base stations 1-2 and 1-3.

If it is determined at Step S4-3 that a response packet is not receivedfrom any of the surrounding base stations, that is, N at Step S4-3, theprocess proceeds to Step S4-5 described below.

If, otherwise, the determination at Step S4-3 is Y, i.e., if a responsepacket is received from any of the surrounding base stations, the uniqueinformation of the surrounding base station inserted in the payloadsection of the response packet is extracted, the unique informationincluding the scramble code currently used in this base station, thechip timing of the scramble code, and the number of hops to this basestation, and the extracted base station unique information isstored/updated in the scramble code management table 2-41 of the basestation 1-1 at Step S4-4.

After storing the base station unique information in the scramble codemanagement table 2-41, the base station 1-1 determines whether thepredetermined time has elapsed based on the timer at Step S4-5.

If the determination at Step S4-5 is negative, i.e., the timer has notexpired, it is determined whether all responses to the collection packethave been received at Step S4-6.

If the determination at Step S4-6 is negative, i.e., all the responsepackets are not received, the process returns to Step S4-3.

On the other hand, if the determination at S4-6 is affirmative, i.e.,all response packets have been received, the process proceeds to StepS4-7, wherein a scramble code and chip timing of the scramble code thatdo not overlap with the scramble codes and the chip timing of thescramble codes currently used by the surrounding base stations areselected for the base station 1-1. Here, if the number of scramble codescollected exceeds the number of scramble code repetitions of the CDMAcellular system, a scramble code for the base station 1-1 is randomlyselected from the scramble codes used by surrounding base stations forwhich the number of hops is the greatest (long repetition distance).

Further, when the predetermined period from when the timer is started atStep S4-5 expires, the process proceeds to Step S4-7. At Step S4-7, thescramble code of the base station 1-1 and the chip timing thereof areselected in such a way that the scramble codes currently used by thesurrounding base stations as collected during the predetermined periodmay not be overlapped. In the case that the number of the collectedscramble codes is greater than the number of scramble code repetitionsof the CDMA cellular system, a scramble code for the base station 1-1 israndomly selected from the scramble codes used by surrounding basestations for which the number of hops is the greatest (long repetitiondistance).

Next, operations of the base station that receives the collection packetis explained with reference to FIG. 5.

When the base station 1-1 receives a collection packet from one of thesurrounding base stations, the following process is performed. Namely,at Step S5-1, the base station 1-1 extracts the scramble code and thechip timing thereof currently used by the base station 1-1, and theremaining number of hops provided in the header of the collection packetfrom the surrounding base station. The scramble code, the chip timingthereof, and the remaining number of hops are to be inserted to thepayload section of the response packet to be transmitted.

At Step S5-2, the base station generates a response packet, the basestation having extracted the scramble code, the chip timing thereof, andthe remaining number of hops provided in the header section of thereceived collection packet. Specifically, a destination address, whichis the source address (SA) of the collection packet, is provided to theheader of the response packet, and the scramble code currently used bythe base station 1-1, the chip timing thereof, and the number of hops ofthe base station 1-1 computed based on the remaining number of hops areprovided to the payload section of the response packet.

Then, at Step S5-3, the response packet generated as above istransmitted to the surrounding base station from which the collectionpacket is received.

Next, the mobile communications system according to the secondembodiment of the present invention is explained with reference toFIG. 1. A base station of the mobile communications system according tothe second embodiment recognizes the scramble codes currently used bythe surrounding base stations using communications between base stationsas in the first embodiment, and autonomously and optimally sets up ascramble code unique to the base station.

The mobile communications system according to the embodiment includestwo or more base stations (BS) 1-1, 1-2, 1-3, two or more mobilestations (MS) 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and a network (communicationnetwork) 1-10 to which the base stations are connected.

The base station 1-1, 1-2, and 1-3 form service areas 1-11, 1-21, and1-31, respectively, such that communication services are provided forand between the mobile stations 1-4, 1-5, 1-6, 1-7, 1-8, and 1-9.Communications between a mobile station and a base station of a servicearea are carried out by frequency-division duplex transmission (FDD),wherein an uplink circuit uses a frequency different from a downlinkcircuit. Further, a code division multiple access method (CDMA) is usedin the uplink circuit such that more than one mobile station can makesimultaneous access to the base station, using different orthogonalcodes.

Further, in order that the mobile stations 1-4, 1-5, 1-6, 1-7, 1-8, and1-9 may identify a base station that serves the service area to whicheach of the mobile stations belongs, a unique identifier (scramble code)is assigned to each of the base stations 1-1, 1-2, and 1-3.

In the CDMA cellular system according to the present embodiment, Nscramble codes are prepared, which are repeatedly assigned to the basestations.

Next, the base station of the mobile communications system according tothe present embodiment is explained with reference to FIG. 6 and FIG. 7.The base station 1-1 includes a CPU 6-1, ROM 6-2, RAM 6-3, a datastorage unit 6-4, a network communications unit 6-5, a GPS receivingunit 6-6, and a radio communicating unit 6-7, all of which are connectedthrough a bus as shown in FIG. 6.

The CPU 6-1 controls operations of the base station 1-1 according to aprogram stored in ROM 6-2. ROM 6-2 stores the program that the CPU 6-1executes. RAM 6-3 stores data required for the program execution by theCPU 6-1. The data storage unit 6-4 stores a scramble code managementtable that includes permanent data required for the mobilecommunications system, and unique information of the surrounding basestations such as the base stations 1-2 and 1-3.

An example of the scramble code management table 6-41 is shown in FIG.7. The scramble code management table 6-41 holds an identifier uniquelyassigned to each of the surrounding base stations, which can be a MAC(Media Access Control) address or an IP (Internet Protocol) address, anidentifier of the scramble codes currently used by the respective basestations, chip timing of the scramble codes, and the distance betweenthe base station 1-1 and each of the surrounding base stations.

Although it is desirable that the base station 1-1 be equipped with theGPS receiving unit 6-6, it is dispensable. When the GPS receiver is notprovided, the geographical position of the base station 1-1 is manuallyinput. In the case that the GPS receiver is provided, a pseudo random(PN) sequence number transmitted from the GPS (Global PositioningSystem) is received, and an arithmetic operation is performed such thatthe position of the base station 1-1 is acquired.

The radio communicating unit 6-7 carries out radio communications withmobile stations through an antenna 6-8. The radio communicating unit 6-7performs processes peculiar to radio communications, such asscrambling/de-scrambling, error correcting, coding/decoding, andmodulating/demodulating processes.

Further, the CPU 6-1 includes a scramble code selecting unit 7-1, aninformation updating unit 7-2 connected to the scramble code selectingunit 7-1, a packet information extracting unit 7-3 connected to theinformation updating unit 7-2, a packet transceiver unit 7-4 connectedto the packet information extracting unit 7-3, a geographic informationacquiring unit 7-5, an unique information extracting unit 7-6, a packetgenerating unit 7-7 connected to the unique information extracting unit7-6 and the packet transceiver unit 7-4 as shown in FIG. 7.

The scramble code selecting unit 7-1 of the base station 1-1 assigns ascramble code and chip timing thereof to be used by the base station 1-1in such a way that the selected scramble code and the chip timingthereof are not used by the surrounding base stations, referring to thescramble code management table 6-41.

When a response packet is received from one of the surrounding basestations, the response packet containing a scramble code identifier, thechip timing thereof, and the number of hops between the base station 1-1and the surrounding base station, the information updating unit 7-2updates the scramble code, the chip timing thereof, and the number ofhops to the surrounding base station stored in the scramble codemanagement table 6-41 with the new information.

In the case of the base station 1-1 receiving a collection packet from asurrounding base station, the packet information extracting unit 7-3extracts the base station unique information of the base station 1-1,which is then inserted in the payload section of a response packet (theposition information of the base station 1-1, and response determiningthreshold). The response determining threshold is typically set atseveral km. On the other hand, in the case that the base station 1-1receives a response packet from a surrounding base station, the basestation unique information of the surrounding base station inserted inthe payload section of the response packet (a scramble code, chip timingof the scramble code, and distance between the base stations) isextracted.

The packet transceiver unit 7-4 performs transmission and reception of apacket with the network communications unit 6-5. Further, in the packettransceiver unit 7-4, a process peculiar to network communications isperformed so that the communications with the network communicationsunits 6-5 are provided.

Information about the position of the base station 1-1 is provided tothe geographic information acquiring unit 7-5. When a GPS receiver isnot provided, the position information is manually input. If the GPSreceiver is provided, which is a desired configuration, the positioninformation is acquired by an arithmetic operation by the GPS receivingunit using the Global Positioning System.

The unique information extracting unit 7-6 of the base station 1-1extracts the base station unique information of the base station 1-1required for generation of a collection packet or a response packet. Thepacket generating unit 7-7 generates the collection packet forcollecting the base station unique information of other base stations,when the base station 1-1 is initiated. On the other hand, when the basestation 1-1 receives a collection packet, a response packet in responseto the collection packet is generated.

Next, an operations flow of the base station 1-1 of the mobilecommunications system according to the present embodiment is explainedwith reference to FIG. 8 and FIG. 9.

When the base station 1-1 is initiated such as by turning on the powersupply, the following process is carried out. Namely, at Step S8-1, thebase station 1-1 generates a collection packet in order to collect basestation unique information of the surrounding base stations such as thebase stations 1-2 and 1-3. At this time, a broadcast address is set intothe header of the collection packet as the destination address. Further,the payload section of the collection packet is provided with geographicinformation of the base station 1-1 acquired by the geographicinformation acquiring unit 7-5, and a response determining threshold.The response determining threshold defines a range of surrounding basestations (distance from the base station 1-1 to the surrounding basestations), which base stations are requested to provide a responsepacket.

Then, at Step S8-2, the generated collection packet is broadcast to thesurrounding base stations currently installed in the CDMA cellularsystem using facilities for communications between base stations. Inthis manner, the base station does not have to receive a pilot channelor a sync channel from other base stations; regardless of theinstallation situation of other base stations, a collection packet canbe transmitted to base stations in a wide area, and the base stationunique information of the base stations in the wide range can becollected.

Further, when the collection packet is broadcast, the timer formeasuring elapsed time is started at Step S8-2.

The base station 1-1 that broadcasts the collection packet to thesurrounding base stations currently installed on the CDMA cellularsystem determines whether a response packet has been received from anyof the surrounding base stations at Step S8-3.

If it is determined that the response packet is not received from any ofthe surrounding base stations (Step S8-3: N), the process proceeds tostep S8-5 that is described below.

Otherwise, if it is determined that a response packet is received fromone of the surrounding base stations at Step S8-3 (Step S8-3:Y), thebase station unique information of the surrounding base station insertedin the payload section of the response packet is extracted. The basestation unique information includes an identifier of the scramble codecurrently used by the surrounding base station, the chip timing thereof,and the distance to the surrounding base station, or geographicinformation. The extracted base station unique information is stored inthe scramble code management table of the base station 1-1 at Step S8-4.

Further, it is determined whether the predetermined period has elapsedbased on the timer at Step S8-5.

If it is determined at Step S8-5 that the predetermined period has notelapsed, the process proceeds to Step S8-6 where it is determinedwhether all responses to the collection packet have been received.

If it is determined at Step S8-6 that all the response packets to thecollection packet are not received, the process returns to Step S8-3.

Otherwise, if it is determined that all the response packets to thecollection packet have been received, the process proceeds to Step S8-7.At Step S8-7, a scramble code and the chip timing thereof are selectedfor the base station 1-1 in such a way that the scramble code and thechip timing thereof of the base station 1-1 do not overlap with those ofthe surrounding base stations based on the base station uniqueinformation collected by that time. Here, in the case that the number ofthe collected scramble codes is greater than the number of scramble coderepetitions of the CDMA cellular system, a scramble code for the basestation 1-1 is randomly selected from the scramble codes used by thesurrounding stations the distance of which is the greatest (longrepetition distance).

Further, if it is determined that the predetermined period has beenelapsed at Step S8-5, the process proceeds to Step S8-7. At Step S8-7,the scramble code and the chip timing of the base station 1-1 areselected in such a way that they do not overlap with the scramble codesand the chip timing currently used by the surrounding base stationscollected by that time, i.e., at the timer expiration time. Here, in thecase that the number of the collected scramble codes is greater than thenumber of scramble code repetitions of the CDMA cellular system, ascramble code for the base station 1-1 is randomly selected from thescramble codes used by the surrounding stations the distance of which isthe greatest (long repetition distance).

Next, operations of the base station when it receives the collectionpacket are explained with reference to FIG. 9.

The base station 1-1 performs the following process when a collectionpacket is received from one of surrounding base stations. Namely, atStep S9-1, the base station 1-1 extracts geographic information and aresponse determining threshold of the surrounding base station insertedin the payload section of the collection packet that is received.

Then, at Step S9-2, the distance between the surrounding base stationand the base station 1-1 is computed based on the geographic informationextracted from the collection packet of the surrounding base station andthe geographic information of the base station 1-1. Next, at Step S9-3,it is determined whether the computed distance is smaller than theextracted response determining threshold.

If it is determined at Step S9-3 that the computed distance between thebase stations is greater than the extracted response determiningthreshold, the process ends.

Otherwise, if it is determined at Step S9-3 that the computed distancebetween the base stations is less than the response determiningthreshold, the process proceeds to Step S9-4, wherein a response packetis generated. Specifically, the source address (SA) of the collectionpacket is extracted and provided to the destination address of theheader of the response packet, and identifiers of the scramble code andchip timing thereof currently used by the base station 1-1, and thecomputed distance between the base stations are inserted in the payloadsection of the response packet.

Next, at Step S9-5, the generated response packet is transmitted to thesurrounding base station from which the collection packet is received.

Although the cases where scramble codes, and the like of the surroundingbase stations are collected when initiating a base station in the firstand the second embodiments above, the base station can be set up with ascramble code that is determined in advance using the method asdescribed above.

The mobile communications system according to the third embodiment ofthe present invention is explained with reference to FIG. 1.

The mobile communications system according to the present embodimentautonomously sets up a scramble code unique to a base station based onscramble codes used by surrounding base stations, the scramble codesbeing collected by mobile stations.

The mobile communications system 1 according to the present embodimentincludes two or more mobile stations 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, twoor more base stations 1-1, 1-2, 1-3, and a network 1-10 to which thebase stations are connected like the embodiments mentioned above.

In order for the base stations 1-1, 1-2, and 1-3 to providecommunications with the mobile stations 1-4, 1-5, 1-6, 1-7, 1-8, and1-9, service areas 1-11, 1-21, and 1-31 are formed. Here, in the serviceareas 1-11, 1-21, and 1-31 formed by the base stations 1-1, 1-2, and1-3, respectively, the communications are performed with the mobilestations 1-4, 1-5, 1-6, 1-7, 1-8, and 1-9 using the code divisionmultiple access. Further, an identifier is assigned to each of the basestations 1-1, 1-2, and 1-3 such that the mobile stations 1-4, 1-5, 1-6,1-7, 1-8, and 1-9 can identify the base stations 1-1, 1-2, and 1-3.

In the mobile communications system according to the present embodiment,N×M scramble codes are available, where N and M are positive integers.The N×M scramble codes are divided into N scramble code groups, eachscramble code group containing M scramble codes. Each scramble codegroup is assigned an identifying number from 1 to N. In the followingdescription of the present embodiment, the scramble code group number 1is selected as a first choice by a base station that is newly installedusing plug-and-play.

Hereafter in embodiments 3 and 4, the base station 1-2 and the mobilestation 1-4 are taken as the target base station and the target mobilestation, respectively, for explanations. Since the base stations 1-1 and1-3 are configured the same as the base station 1-2, and the mobilestations 1-5, 1-6, 1-7, 1-8, and 1-9 are configured the same as themobile station 1-4, the explanations thereof are not repeated.

Next, the base station 1-2 of the mobile communications system accordingto the present embodiment is explained with reference to FIG. 10 andFIG. 11. The base station 1-2 is equipped with a CPU 10-1, ROM 10-2, RAM10-3, a data storage unit 10-4, and a radio communicating unit 10-5, allof which are connected through a bus as shown in FIG. 10.

The CPU 10-1 controls operations of the base station 1-2 according to aprogram stored in ROM 10-2. ROM 10-2 stores the program that the CPU10-1 executes. RAM 10-3 stores data required for the program executionby the CPU 10-1. The data storage unit 10-4 stores a scramble codemanagement table that contains permanent data required for the mobilecommunications system, and identifiers of scramble codes and chip timingthereof of the surrounding base stations such as the base stations 1-1and 1-3.

An example of the scramble code management table 10-41 is shown in FIG.11. The scramble code management table 10-41 contains MAC addresses orIP addresses of the surrounding base stations, scramble code numbers andchip timing thereof used by the base stations, and other scramble codenumbers and chip timings.

The radio communicating unit 10-5 performs radio communications with themobile stations through an antenna 10-6. The radio communicating unit10-5 performs processes peculiar to the radio communications, such asscrambling/de-scrambling, error correcting, encoding/decoding, andmodulating/demodulating such that radio communications with the mobilestations are provided.

Further, the CPU 10-1 includes a scramble code selecting unit 11-1, aninformation updating unit 11-2 connected to the scramble code selectingunit 11-1, and a packet control unit 11-3 connected to the informationupdating unit 11-2 as shown in FIG. 11.

The scramble code selecting unit 11-1 of the base station 1-2 selects ascramble code and chip timing thereof to be used by the base station 1-2in such a way that the scramble code and the chip timing thereof are notoverlapped with the surrounding base stations 1-1 and 1-3, referring tothe scramble code management table 10-41.

The information updating unit 11-2 stores the base station address, ascramble code, and the chip timing of the scramble code of thesurrounding base stations reported by the mobile station 1-4 andextracted by the packet control unit 11-3 (described below) in thescramble code management table 10-41. Further, the information updatingunit 11-2 extracts the base station address, the scramble code, and thechip timing of the scramble code of the surrounding base stations fromthe scramble code management table 10-41 in order to provide the basestation unique information collected by this time to the mobile station1-4.

When the scramble codes currently used by other base stations arereported by the mobile station 1-4, the packet control unit 11-3extracts the base station unique information contained in the payloadsection of the packets received. Further, the packet control unit 11-3generates a packet for providing the base station unique informationcollected to the mobile station 1-4.

Next, the mobile station 1-4 of the mobile communications systemaccording to the present embodiment is explained with reference to FIG.12 and FIG. 13. The mobile station 1-4 of the mobile communicationssystem according to the present embodiment includes a CPU 12-1, ROM12-2, RAM 12-3, a data storage unit 12-4, and a radio communicating unit12-5, all of which are connected through a bus as shown in FIG. 12.

The CPU 12-1 controls operations of the mobile station 1-4 according toa program stored in ROM 12-2. ROM 12-2 stores the program that the CPU12-1 executes. RAM 12-3 stores data required for the program executionby the CPU 12-1. The data storage unit 12-4 stores permanent datarequired for the mobile communications system, and a scramble codemanagement table.

An example of the scramble code management table 12-41 is shown in FIG.13. The scramble code management table 12-41 contains a MAC address oran IP address of surrounding base stations, and a scramble code # andchip timing thereof used by the surrounding base stations.

The radio communicating unit 12-5 performs radio communications with thebase station 1-2 through an antenna 12-6. In order to perform the radiocommunications, the radio communicating unit 12-5 performs processespeculiar to radio communications, such as scrambling/de-scrambling,encoding/decoding, and modulating/demodulating.

Further, the CPU 12-1 includes a scramble code identifying unit 13-1, aninformation updating unit 13-2, and a packet control unit 13-3 connectedto the information updating unit 13-2 as shown in FIG. 13.

The scramble code identifying unit 13-1 identifies scramble codes andthe chip timing thereof used by surrounding base stations when themobile station is to perform a hand-off process.

The information updating unit 13-2 stores the base station uniqueinformation (the base station address, the scramble code uniquelyassigned to the base station, and chip timing of the scramble code)provided by the base station 1-2 extracted by the packet control unit13-3 (described below) in the scramble code management table 12-41.Further, the address of the target base station 1-2, with which themobile station is communicating, which is identified by the scramblecode identifying unit 13-1, the scramble code, and the chip timing ofthe scramble code assigned to the target base station 1-2 are stored.Furthermore, the base station address, the scramble code, and the chiptiming thereof are extracted from the scramble code management table12-41, and are transmitted to the target base station 1-2 when thehand-off process is to take place.

When the target base station 1-2 provides a packet containing thescramble codes currently used by the surrounding base stations 1-1 and1-3, the packet control unit 13-3 extracts for each base station theaddress, the scramble code assigned to the base station, and the chiptiming thereof from the packet. Further, when the mobile station 1-4 isto perform the hand-off process, a report packet is generated. Thereport packet contains the base station addresses of the surroundingbase stations collected by the target base station 1-2 in advance of thehand-off to the base station of the hand-off destination. The reportpacket further contains the scramble codes assigned to the surroundingbase stations, and the chip timing of the scramble codes.

Next, the operations flow of the base station of the mobilecommunications system according to the present embodiment is explainedwith reference to FIG. 14.

The base station 1-2 performs the following process when beinginitiated. Namely, at Step S14-1, in the case that the base station 1-2is newly installed, the base station 1-2 randomly selects a scramblecode from the M scramble codes contained in the scramble code group #1as mentioned above. Further, the base station 1-2 randomly sets up thechip timing of the scramble code.

In this manner, an initial scramble code differentiated from scramblecodes for service is set up, and the scramble code of the base station1-2 and chip timing thereof are not overlapped with those of thesurrounding base stations.

Then, at Step S14-2, the base station 1-2 starts providing the servicein the service area concerned with the initial scramble code and thechip timing thereof. Further, a timer is started in order to measureelapsed time when starting the service.

Then, at Step S14-3, it is determined whether the mobile station 1-4 isproviding information about surrounding base stations such as the basestations 1-1 and 1-3, the information containing a base station address,a scramble code identifier, and a chip timing identifier.

If the determination at Step S14-3 is negative, i.e., there is no reportconcerning the base station address, the scramble code, and the chiptiming thereof of the surrounding base stations, the process proceeds toStep S14-6, which is described below.

Otherwise, if the determination at Step S14-3 is affirmative, i.e.,there is a report from the mobile station 1-4 concerning the basestation address, the scramble code, and the chip timing thereof of thesurrounding base stations 1-1 and 1-3, the process proceeds to StepS14-4. At Step S14-4, the base station address, the scramble code, andthe chip timing thereof of the base stations 1-1 and 1-3 are stored inthe scramble code management table 10-41 of the base station 1-2. Then,at Step S14-5, the base station 1-2 provides the mobile station 1-4 withthe information collected so far about the scramble codes and the chiptiming thereof used by the base stations 1-1 and 1-3.

Next, at Step S14-6, it is determined whether the predetermined periodhas expired based on the timer of the base station 1-2, which is startedsimultaneously with the service start. If the determination at StepS14-6 is negative, i.e., the predetermined period has not elapsed, theprocess returns to Step S14-3. Otherwise, if the determination at StepS14-6 is affirmative, the process proceeds to Step S14-7. At Step S14-7,a new scramble code and chip timing thereof for the base station 1-2 areselected. The new scramble code is selected from the scramble codegroups #2 through #N in such a way that the new scramble code and chiptiming thereof for the base station 1-2 do not overlap with those ofsurrounding base stations for which the report has been received duringthe predetermined period.

Next, the operations flow of the mobile station 1-4 of the mobilecommunications system according to the present embodiment is explainedwith reference to FIG. 15.

When the mobile station 1-4 starts hand-off processing, it also performsthe following process. Namely, at Step S15-1, the mobile station 1-4provides a hand-off destination base station, such as the base stations1-1 and 1-3 with information. The information includes base stationaddresses of base stations that surround the base station 1-2, which isthe base station currently in contact, and scramble codes and chiptiming thereof used by the surrounding base stations. The informationfurther includes the address of the base station currently in contact,and the scramble code and chip timing thereof of the base station incontact. Here, the information is stored in the scramble code managementtable 4-41 of the mobile station 1-4.

Next, at Step S15-2, the mobile station 1-4 determines whether there isa report from the hand-off destination base station such as the basestations 1-1 and 1-3, the report containing addresses of base stationsthat surround the hand-off destination base station, scramble codeidentifiers, and identifiers of the chip timing of the scramble codes.

If the determination at Step S15-2 is negative, i.e., if there is noreport, the process is ended. If, otherwise, the determination at StepS15-2 is affirmative, i.e., if there is a report, the contents arestored in the scramble code management table 4-41 of the mobile station1-4.

In this manner, the base station 1-2 can collect the base station uniqueinformation of the surrounding base stations at a first position, asecond position, a third position and so on by a mobile stationcollecting the base station unique information and transmitting the sameto the base station 1-2 while moving, and a long repetition distance ofthe scramble code (ensuring a long distance between base stations usingthe same scramble code), and the like, can be set up.

In the present embodiment, the scramble codes are divided into Nscramble code groups, each group consisting of M scramble codes.Nevertheless, the scramble codes do not have to be divided into scramblecode groups. In this case, a scramble code that is used exclusively atan initial operation of a base station is pre-assigned.

Next, the mobile communications system according to the fourthembodiment of the present invention is explained.

According to the third embodiment, a scramble code is beforehand setaside for initial setting of a base station. Here, according to thefourth embodiment, the scramble code for initial setting is determinedby a predetermined method.

The mobile communications system according to the present embodiment hasthe same configuration as the foregoing embodiments as explained withreference to FIG. 1, and consists of two or more mobile stations 1-4,1-5, 1-6, 1-7, 1-8, 1-9, two or more base stations 1-1, 1-2, 1-3, and anetwork 1-10 to which the base station are connected.

In order for the base station 1-1, 1-2, and 1-3 to providecommunications with the mobile stations 1-4, 1-5, 1-6, 1-7, 1-8, and1-9, service areas 1-11, 1-21, and 1-31, respectively, are formed. Thecommunications in the service areas can use the code division multipleaccess (CDMA).

Further, a unique identifier is assigned to each of the base stations1-1, 1-2, and 1-3 such that the mobile stations 1-4, 1-5, 1-6, 1-7, 1-8,and 1-9 can identify the base stations 1-1, 1-2, and 1-3.

The CDMA cellular system according to the present embodiment isexplained using the case where L scramble codes (L is a positiveinteger) are available. Further, in the present embodiment, when a basestation is installed using plug and play, scramble codes are not dividedinto scramble code groups. Rather, in the present embodiment, a defaultscramble code is set up out of the L scramble codes according to apredetermined method.

First, the predetermined method of determining a scramble code in theinitial stage of a base station installation in the mobilecommunications system according to the present embodiment is explained.

The following methods are available for determining a scramble code tobe used in the initial stage (initial scramble code).

-   -   (1) The first method is to select a scramble code randomly from        the L scramble codes.    -   (2) The second method is to determine a scramble code by        performing a predetermined arithmetic operation, using the base        station unique information.    -   (3) The first example of the second method is to use the MAC        address or IP address assigned to the base station.    -   (4) The second example of the second method is to use position        information acquired by a GPS receiver, if one is installed.    -   (5) The third example of the second method is to use the time        (e.g., HH:MM:SS) at which the base station is initiated.

Here, the first example of the second method is explained, where a MACaddress is assumed available. Suppose that the MAC address of the basestation is 00:06:5B:87:DF:8D. Further, the number L of scramble codesavailable to the CDMA cellular system is set to L=256.

1) The lowest octet of the MAC address is extracted, which is 8D.

Then, an arithmetic operation is carried out on the octet 8D to obtain adecimal value 141.

2) Three lowest octets are treated separately, a summing operation iscarried out on the three octets, and a MOD operation (surplus operation)is carried out on the sum.

Specifically, the three low octets are 87, DF, and 8D. Here, 87 inhexadecimal is converted into binary to give 10000111, which is equal to145 in decimal. Further, DF in hexadecimal is converted into binary togive 11011111, which is equal to 223 in decimal. Further, 8D inhexadecimal is converted into binary to give 10001101, which is equal to141 in decimal. Accordingly,

MOD((145+223+141),256)=243

As above, 243 is obtained as a result of the arithmetic operation.

3) Treat the lowest 3 octets separately, and an exclusive OR (XOR) istaken. The XOR of 87, DF, and 8D, which are 10000111, 11011111, and10001101, respectively, is as follows.

10000111+11011111+10001101=11010101

Therefore, 213 is obtained as a result of the arithmetic operation.

4) The MAC address is bit-shifted to the left or to the right randomly.For example, the MAC address 00:06:5B:87:DF:8D is shifted to the left by4 bits, 00:65:B8:7 D:F8:D0 is obtained. Accordingly, the lowest octet D0is obtained.

Therefore, 208 in decimal is obtained as a result of the arithmeticoperation.

5) An operation of MD5 (Message Digest 5) Hash Function (output of fixedlength is obtained from input of variable length) is performed. As forthe MD5 Hash Function, an input can take any length, and, as for anoutput, a 128 bit long string is output. The 128 bit string is convertedinto an 8 bit string by performing operations 1) through 4) above.

Alternatively, a Hash Function other than the MD5 Hash Function may beused. Further, another Hash Function that outputs an 8 bit string can beused.

Next, the base station of the mobile communications system according tothe present embodiment is explained with reference to FIG. 16 and FIG.17. The base station 1-2 is equipped with a CPU 16-1, ROM 16-2, RAM16-3, a data storage unit 16-4, a network communications unit 16-5, aGPS receiving unit 16-6, and a radio communicating unit 16-7, all ofwhich are connected through a bus as shown in FIG. 16.

The CPU 16-1 controls operations of the base station 1-2 according to aprogram stored in ROM 16-2. ROM 16-2 stores the program that the CPU16-1 executes. RAM 16-3 stores data required for the program executionby CPU 16-1. The data storage unit 16-4 stores permanent data requiredfor the mobile communications system, and a scramble code managementtable.

An example of the scramble code management table 16-41 is shown in FIG.17. The scramble code management table 16-41 contains a MAC address oran IP address of surrounding base stations, scramble code number andchip timing thereof; and the scramble code number and chip timingthereof of the base station 1-2.

The network communications unit 16-5 carries out a process forcommunication between the base stations connected to the mobilecommunications system, for example, a CDMA cellular network, andprovides communications between the base stations. Although it isdesirable that the base station 1-2 be equipped with the GPS receivingunit 16-6, it is not mandatory, especially when the base station isinstalled in a building. The GPS receiving unit 16-6 receives a pseudorandom signal from the GPS (Global Positioning System), and the positionof the base station 1-2 is computed.

The radio communicating unit 16-7 performs radio communications withmobile stations through an antenna 16-8. The radio communicating unit16-7 performs processes peculiar to the radio communications, such asscrambling/de-scrambling, error correcting, encoding/decoding, andmodulating/demodulating such that the radio communications with themobile stations are provided.

Further, the CPU 16-1 includes a scramble code selecting unit 17-1, aninformation updating unit 17-2 connected to the scramble code selectingunit 17-1, a packet control unit 17-3 connected to the informationupdating unit 17-2, and an information analyzing unit 17-4 connected tothe packet control unit 17-3 and to the scramble code selecting unit17-1 as shown in FIG. 17.

The scramble code selecting unit 17-1 selects a scramble code and chiptiming of the scramble code to be used by the base station 1-2 in such away that the scramble code and the chip timing of the base station 1-2do not overlap with those of the surrounding base stations such as thebase stations 1-1 and 1-3 with reference to the management table 16-41.

The information updating unit 17-2 stores the base station uniqueinformation (base station addresses, scramble code identifiers, and chiptiming thereof of surrounding base stations) reported by the mobilestation 1-4 and extracted by the packet control unit 17-3 (describedbelow) in the scramble code management table 16-41. Further, theinformation updating unit 17-2 extracts the base station addresses, thescramble code identifiers, and the chip timing thereof of thesurrounding base stations from the scramble code management table 16-41such that the base station unique information is transmitted to themobile station 1-4.

The packet control unit 17-3 extracts the address of the surroundingbase stations, the scramble code, and chip timing of the scramble codeinserted in the payload section of the reported packet provided by themobile station 1-4. Further, the packet control unit 17-3 generates anotice packet for providing the base station address, the scramble code,and the chip timing thereof of the surrounding base stations such as thebase station 1-1 and 1-3, the above-mentioned information having beencollected by this time. The information analyzing unit 17-4 analyzeswhether the mobile station 1-4 reports incommunicability, i.e., thatcommunications cannot be maintained.

Next, the mobile station 1-4 of the mobile communications systemaccording to the present embodiment is explained with reference to FIG.18 and FIG. 19. The mobile station 1-4 of the mobile communicationssystem according to the present embodiment is equipped with a CPU 18-1,ROM 18-2, RAM 18-3, a data storage unit 18-4, and a radio communicatingunit 18-5, all of which are connected through a bus as shown in FIG. 18.

The CPU 18-1 controls operations of the mobile station 1-4 according toa program stored in ROM 18-2. ROM 18-2 stores the program that the CPU18-1 executes. RAM 18-3 stores data required for the program executionby the CPU 18-1. The data storage unit 18-4 stores permanent datarequired for the mobile communications system, and a scramble codemanagement table.

An example of the scramble code management table 18-41 is shown in FIG.19. The scramble code management table 18-41 contains a MAC address oran IP address, a scramble code #, and chip timing thereof used bysurrounding base stations.

The radio communicating unit 18-5 performs radio communications with thebase station 1-2 through an antenna 18-6. The radio communicating unit18-5 performs processes peculiar to radio communications, such asscrambling, error correcting, encoding, modulating, and demodulatingsuch that the radio communications with the base station 1-2 areprovided.

Further, the CPU 18-1 includes a scramble code identifying unit 19-1, aninformation updating unit 19-2, a packet control unit 19-3 connected tothe information updating unit 19-2, and a communication situationmonitoring unit 19-4 connected to the packet control unit 19-3, as shownin FIG. 19.

When the mobile station 1-4 carries out the hand-off, the scramble codeidentifying unit 19-1 identifies the scramble code and the chip timingthereof currently used by the surrounding base stations such as the basestations 1-1 and 1-3.

The information updating unit 19-2 stores in the scramble codemanagement table 18-41 the base station address, the scramble codeidentifier, and the chip timing thereof of the surrounding base stationthat is the hand-off destination, the base station address, the scramblecode identifier, and the chip timing thereof being extracted by thepacket control unit 19-3. Further, the base station address, thescramble code identifier, and the chip timing thereof of the basestation 1-2 with which the mobile station is in communication asidentified by the scramble code identifying unit 19-1 are stored.Furthermore, the surrounding base stations addresses, the scramblecodes, and the chip timing thereof are extracted from the scramble codemanagement table 18-41 for reporting to the base station 1-2.

When a packet containing identifiers of the scramble codes currentlyused by the base stations surrounding the base station 1-2 is received,the packet control unit 19-3 extracts the base station address, thescramble code identifier, and the chip timing thereof of the surroundingbase station that is the hand-off destination from the packet. Further,when a hand-off process of the mobile station 1-4 is carried out, apacket for reporting the base station unique information collected tothe base station of the hand-off destination is generated. Furthermore,when the mobile station 1-4 cannot communicate, a packet for reportingthe communication failure is generated, and the packet is transmitted tothe base station with which the communication is ongoing.

The communication situation monitoring unit 19-4 determines whether thesignal from the base station of communication failure is correctlyrestored in the radio communicating unit 10-5.

Next, the operations flow of the base station of the mobilecommunications system according to the present embodiment is explainedwith reference to FIG. 20 and FIG. 21.

When the base station is 1-2 initiated, the following process isperformed. Namely, at Step S20-1, the base station 1-2 selects ascramble code and chip timing of the scramble code by the initialscramble code-selection method mentioned above, using, for example, thebase station unique information (MAC address).

Next, at Step S20-2, a service is started being provided to the servicearea of the base station 1-2 using the selected scramble code and thechip timing thereof. Further, a timer is started in order to measure theelapsed time from the service start.

After the service is started, at Step S20-3, it is determined whetherthere is a report from any mobile station concerning the address, ascramble code, and the chip timing of this scramble code of surroundingbase stations.

If it is determined at Step S20-3 that there is a report concerning thebase station address, the scramble code, and the chip timing thereoffrom other base stations such as the base stations 1-1 and 1-3, theprocess proceeds to Step S20-4. At Step S20-4, the base station 1-2stores the base station address, the scramble code, and the chip timingthereof in the scramble code management table 8-41 of the base station1-2. At the same time, at Step S20-5, the base station 1-2 provides thebase station address, the scramble code, and the chip timing thereof ofthe surrounding base stations collected so far to the reporting mobilestation. Then, at Step S20-6, the base station 1-2 determines whether apredetermined period has elapsed based on the timer that is startedsimultaneously with the service start.

If it is determined at Step S20-6 that the predetermined period haselapsed, the process proceeds to Step S20-7. At Step S20-7, whether atleast one report concerning the base station unique information (thebase station address, the scramble code, and chip timing thereof) isreceived from any mobile station during the predetermined period isdetermined.

If the determination at Step S20-7 is affirmative, it can be determinedthat there is no duplication of the scramble code, that communication ispossible, and the process is ended.

On the other hand, if a report has not been received from any mobilestation even once, i.e. No at Step S20-7, the scramble code of the basestation 1-2 is determined to be overlapped/duplicated with another basestation, and communication is not possible. Then, the process proceedsto step S20-11. At Step S20-11, a new scramble code is randomlyselected. More desirably, a new scramble code is selected in such a waythat the new scramble code is not being used by the surrounding basestations.

On the other hand, if it is determined at Step S20-6 that thepredetermined time has not elapsed according to the timer that isstarted simultaneously with the service start, the process returns toStep S20-3. Further, if it is determined at Step S20-3 that there is noreport from any mobile station concerning the base station addresses,the scramble codes, and the chip timing thereof of other base stations,the process proceeds to Step S20-8. At Step S20-8, it is determinedwhether there is any report of incommunicability from any mobilestation.

If the determination at Step S20-8 is negative, i.e., there is no reportof incommunicability from any mobile station, the process proceeds toStep S20-6.

On the other hand, if the determination at Step S20-8 is affirmative,i.e., a mobile station reports incommunicability, the base station 1-2generates a collection packet for collecting the base station uniqueinformation (a scramble code, and chip timing thereof currently used) ofthe surrounding base stations such as the base stations 1-1 and 1-3. Thecollection packet also contains the identifier of the scramble code usedby the base station 1-2 in the payload section. Then, at Step S20-9, thecollection packet is broadcast to base stations currently installed onthe CDMA cellular system using the between-base-station communicationfacilities.

The base station 1-2, having broadcast the collection packet, determineswhether a response packet to the collection packet is received fromother base stations at Step S20-10.

If the determination at Step S20-10 is negative, the process returns toStep S20-3. Otherwise, if the determination at Step S20-10 isaffirmative, the process proceeds to Step S20-11. At Step S20-11, a newscramble code to be used by the base station 1-2 is reselected fromscramble codes that are not used by other base stations, and the serviceis resumed.

Here, the operations flow of the base station that receives thecollection packet is explained with reference to FIG. 21.

The base station such as the base station 1-1 or 1-3 that receives thecollection packet extracts the scramble code of the base station 1-2inserted in the payload section of the collection packet at Step S21-1.

At Step S21-2, the base station such as the base station 1-1 or 1-3determines whether the extracted scramble code, i.e. used by the basestation 1-2, is the same as the scramble code currently used by the basestation such as the base station 1-1 or 1-3 as applicable. If thedetermination is negative, i.e., the scramble codes are not the same,the process is ended.

To the contrary, if the determination at Step S21-2 is affirmative,i.e., the two base stations are using the same scramble code, a responsepacket is generated at Step S21-3. The source address (SA) of thecollection packet is made the destination address, and is inserted intothe header section of the generated response packet. The payload sectionof the response packet does not contain any data. Further, although itis not mandatory, if the base station is provided with the GPS receivingunit 8-6, it is desirable to insert the position information(coordinates) of the base station or the distance between the basestations in the payload section.

Then, at Step S21-4, the generated response packet is transmitted to thebase station 1-2 that has sent out the collection packet.

Next, the operations flow of the mobile station 1-4 of the mobilecommunications system according to the present embodiment is explainedwith reference to FIG. 22 and FIG. 23.

At Step S22-1, the mobile station 1-4 during execution of a hand-offprocess provides the base station of the hand-off destination, such asthe base station 1-1 or 1-3, with the addresses, the scramble codes, andthe chip timing thereof of the surrounding base stations stored in thescramble code management table 18-41 of the mobile station 1-4, thesurrounding base stations surrounding the base station currently incontact, and with the address, the scramble code, and the chip timingthereof of the base station 1-2 currently in contact.

The mobile station 1-4 having provided the base station address, thescramble code, and the chip timing thereof determines whether a basestation address, a scramble code, and the chip timing thereof of basestations surrounding the base station of the hand-off destination arereceived from the hand-off destination base station at Step S22-2.

If it is negatively determined at Step S22-2, the process is ended. Tothe contrary, if the determination at Step S22-2 is affirmative, thebase station address, the scramble code, and the chip timing thereof ofthe surrounding base stations, which surround the base station of thehand-off destination, are stored in the scramble code management table18-41 at Step S22-3.

Here, the operations flow of the mobile station that measurescommunication quality is explained with reference to FIG. 23.

The mobile station that measures the communication quality performs thefollowing process. For example, the present embodiment explains the casewhere a bit error rate is used as the communication quality. However,measurement of the communication quality is not limited to the bit errorrate, but a packet error rate and a Signal to Interference and NoisePower Ratio (SINR) can be used.

At Step S23-1, it is determined whether the value of an observed biterror rate is greater than a threshold value specified by the CDMAcellular system, i.e., whether the bit error rate fulfils the qualityspecified by the CDMA cellular system.

If the determination at Step S23-1 is that the bit error rate at themobile station 1-4 satisfies the communication quality specified by theCDMA cellular system, the process is ended.

Otherwise, a timer is started at Step S23-2, and the mobile station 1-4continues to observe the bit error rate at Step S23-3. Next, at StepS23-4, it is determined whether a predetermined period has elapsedaccording to the timer is determined.

At Step S23-4, whether the timer is still continuing is determined. Ifthe determination is affirmative, the process returns Step S23-3, andthe bit error rate observation is continued.

On the other hand, if the determination at Step S23-4 is negative, i.e.,the predetermined period has elapsed, and the timer stops, the processproceeds to Step S23-5. At Step S23-5, it is determined whether the biterror rate observed during the predetermined period is constantly poorerthan the communication quality specified by the CDMA cellular system.

If the determination at Step S23-5 is positive, i.e., the communicationquality is not satisfactory, the process proceeds to Step S23-6. At StepS23-6, a reporting packet is generated, which packet is for notifying abase station to which the mobile station belongs (with which the mobilestation is currently in communication) that continuation ofcommunications is impossible. The header of the reporting packet isprovided with a destination address, which is the address of the basestation to which the mobile station belongs. The payload section of thereporting packet contains the information in the context that thecommunications cannot be continued at Step S23-6.

Next, the generated report packet is transmitted to the base station towhich the mobile station belongs at Step S23-7.

On the other hand, if it is determined at Step S23-5 that the poor biterror rate is not a constant phenomenon at the mobile station 1-4, theprocess is ended, and the communication is continued.

In the embodiments described above, the mobile communications systemequipped with three base stations is explained as an example. However,even in the case that the number of the base stations can be more thanthree, assignment of a scramble code, etc., unique to a base station canbe carried out.

APPLICABILITY TO INDUSTRY

The scramble code allocation method according to the present inventionis applicable to a CDMA cellular system, and especially to a basestation using plug-and-play connection, when assigning a scramble code.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

The present application is based on Japanese Priority Application No.filed on Nov. 7, 2003 with the Japanese Patent Office, the entirecontents of which are hereby incorporated by reference.

1. A mobile station of a wireless mobile communications system that includes the mobile station, a plurality of base stations, and a network that connects the base stations, wherein the mobile station that communicates with the base stations discriminates the base stations by identifiers uniquely assigned to each of the base stations, the mobile station comprising: a packet control unit configured to extract unique information used in setting up an identifier of the base stations that surround the base station with which the mobile station is currently communicating, the unique information being extracted from a packet received from the base station with which the mobile station is currently communicating; and an information updating unit configured to store the extracted unique information such that the unique information is updated; wherein the packet control unit provides the stored unique information to the base station with which the mobile station is currently communicating.
 2. The mobile station as claimed in claim 1, further comprising: a communication situation surveillance unit configured to supervise quality of communications with the base station with which the mobile station is currently communicating, and to provide the base station with information reporting that the quality of communications with the base station does not fulfill a predetermined value.
 3. A mobile communication system, comprising: a plurality of base stations; a plurality of mobile stations; and a network that connects the base stations; wherein the mobile stations that communicate with the base stations discriminate base stations by identifiers uniquely assigned to the base stations, each mobile station including a packet control unit configured to extract unique information used in setting up an identifier of the base stations that surround a target base station, the unique information being extracted from a packet received from the target base station; and an information updating unit configured to store the unique information extracted by the packet control unit, the stored unique information being transmitted to the target base station by the packet control unit; the target base station including a packet transceiver unit configured to transmit and receive a packet for collecting the unique information used for setting up the identifier of the base stations that surround the target base station; a packet information extraction unit configured to extract the unique information of the surrounding base stations inserted in the packet that is received; and a scramble code setting unit configured to set up the identifier of the target base station based on the unique information that is extracted by the packet information extracting unit. 